Applicability of AIRS Monthly Mean Atmospheric Water Vapor Profiles over the Tibetan Plateau Region

Abstract

he research explores the applicability of the gridded (level 3) monthly tropospheric water vapor (version 5) retrievals from the Atmospheric Infrared Sounder (AIRS) instrument and the Advanced Microwave Sounding Unit (AMSU) on board the NASA Aqua satellite over the Tibetan Plateau by comparing them with carefully processed radiosonde data. Local correlation analyses indicate that below 200 hPa, the AIRS/AMSU monthly water vapor retrievals are highly consistent with radiosondes over the whole plateau region, especially in the southeastern part and between 300 and 600 hPa. Relative deviation analyses further show that the differences between monthly mean AIRS/AMSU water vapor retrieval data and radiosondes are, in general, small below 250 hPa, in particular between 300 and 600 hPa and in high-altitude areas. Combined with a further direct comparison between AIRS/AMSU water vapor vertical retrievals and radiosonde observations averaged over the entire domain, these results suggest that the gridded monthly AIRS/AMSU water vapor retrievals can provide a very good account of spatial patterns and temporal variations in tropospheric water vapor content in the Tibetan Plateau region, in particular below 200 hPa. However, differences between AIRS/AMSU retrievals and radiosondes are seen at various levels, in particular above the level of 250 hPa. Therefore, for detailed quantitative analyses of water budget in the atmosphere and the entire water cycle, AIRS/AMSU retrieval data may need to be corrected or trained using radiosondes. Two fitting functions are derived for warm and cold seasons, although the seasonal difference is generally small.